1. Field of the Invention
The present invention relates to dentifrice compositions having reduced abrasivity. Specifically, the invention is directed to a method for reducing the abrasivity of dentifrice compositions employing an abrasive system and at least one zinc salt.
2. Description of Related Art
It has been difficult heretofore to provide dentifrices for use in the daily brushing and cleaning of teeth which provide a desirable balance of cleaning and polishing actions. This has been largely due to the difficulty in selecting suitable abrasives which afford maximum removal of difficult stains and debris without damaging the oral hard tissues.
The function of an abrasive substance in formulations intended for use in the oral cavity is to remove various deposits, including pellicle film, from the surface of the teeth. Pellicle film is a tightly adherent film which often contains brown or yellow pigments and imparts an unsightly appearance to the teeth. An advantageous abrasive material for incorporation into dental formulations should maximize film removal without causing undue abrasion to the hard tooth tissues. The typical soft abrasives used in dental compositions, such as dicalcium phosphate and calcium phosphate, although not unduly abrasive to tooth tissue, are not as effective as the hard abrasives in removing these undesirable deposits from the teeth. However, hard abrasives can cause serious problems when present in dental preparations since their outstanding abrasive characteristics are likely to cause undue abrasion to the oral hard tissues (enamel, dentin and cementum).
Others have attempted to address the problem of decreasing the abrasivity of dentifrices. For example, U.S. Pat. No. 4,102,992 discloses dentifrice compositions comprising water-insoluble organic polymers, such as thermoplastic acrylics (polymethyl methacrylate and polyisobutyl methacrylate), cellulosics, polyamides, polyethylene, polystryrene and the vinyls, which are less abrasive than calcium carbonate polishing agent.
U.S. Pat. No. 4,828,833 discloses dentifrice compositions in which a water soluble, linear polymer having a molecular weight above 1,000,000 effects a substantial reduction in dentin abrasivity and improves stain removal.
U.S. Pat. No. 4,144,322 discloses the reduction of enamel abrasiveness in dentifrices comprising a dental abrasive system of hydrated siliceous abrasive and the hard abrasive calcined alumina, and about 1-5% by weight of a calcium, magnesium or sodium salt, which effects a reduction in the radioactive (or relative) enamel abrasion (REA) of the dentifrice.
U.S. Pat. No. 4,407,788 and British Patent No. 2,100,983B disclose a siliceous polishing material and a small amount of a water soluble resinous poly(ethylene oxide) and maltitol humectant, which improve stain removal without raising radioactive (or relative) dentin abrasion (RDA).
Despite the foregoing developments, there is still room in the art for improved dentifrice compositions. In particular, it is desired to provide a method for reducing the abrasivity of dentifrice compositions without unduly hindering their cleaning efficacy. It is also desired to provide dentifrice compositions prepared according to such a method.